In one of our Production host (Linux) there are 5 databases are running under 2 different diskgroups.In that we are seeing huge I/O on DATAFILE_ORPD88 diskgroup. upon checking further we found a SQL from orprd88b & orprd88c database causing this I/O and we suggested application team to create index for that SQL statement.

meanwhile I taken IO statistics report for the diskgroups in that ASM instance it shown like below.in that Bytes read(MB) columns shows value for orprd88c database to nearly 2 TB!!

How did you generate the report? That really dictates what this means.

If the statistics are coming from v$asm_disk, the the values are cumulative since the last restart, meaning it is the total or operations since the ASM instance was last started. That is not a very useful figure.

You can take the approach that is used by statspack age AWR, which is to capture the stats on a regular interval and check the difference between them. Calculating the deltas like this allow you to see the change over time.